The present invention relates to a new and improved method for fault location on a line of the type wherein at least at a measuring location there is formed at least a measurement voltage signal derived from a line voltage and at least a measurement current signal derived from a line current, from such measurement signals there is formed at least one traveling wave signal associated with a traveling wave on the line and its variation with time at the measuring location, and there is formed an evaluation signal characterizing at least the direction of the fault location with respect to the measuring location.
The method of the present invention is an improvement upon that disclosed in the commonly assigned, copending United States application of Otto Lanz and Michael Vitins, filed Apr. 14, 1976, Ser. No. 676,983, entitled "Method And Apparatus For Locating A Fault On A Line", and the disclosure of which is incorporated herein by reference.
There are already known techniques for testing for the presence of a line fault, especially a short-circuit within a predetermined line section, which employ traveling wave signals in the sense previously discussed (U.S. Pat. No. 3,590,368). There such traveling wave signals are formed at both end stations of the line section to be monitored and by means of a special line are correlated to one another for the purpose of fault location.
Furthermore, in the previously mentioned copending application there is described a fault location method wherein at a measuring location there is formed at least one measurement voltage signal derived from a line voltage and at least one measurement current signal derived from a line current and from these measurement signals, by multiplication with different constant factors --especially multiplication of the measurement current signal with a factor corresponding to the wave or characteristic impedance of the line without changing the measurement voltage signal-- as well as by summation with different signs there are formed at least two traveling wave signals of the aforementioned type which are associated with oppositely moving traveling waves on the line, and with which there can be produced an evaluation signal. Formation of the evaluation signal can be accomplished by suitably processing and linking the traveling wave signals such that the sign of the evaluation signal characterizes the direction of the fault location relative to the measuring location and the magnitude of the evaluation signal characterizes the distance of the fault location from the measuring location.
The previously discussed method and others which operate with traveling wave signals for the purpose of determining the fault direction and/or fault distance and also possibly for fault detection on lines, each have the common drawback that the line voltage at the measuring location required for formation of the traveling wave signal and the corresponding measurement voltage signal in the case of short-circuits situated close to the measuring location no longer render possible an error-free evaluation due to voltage breakdown to values close to the disturbance signal peak. Additionally, the functional dependency of the evaluation signal upon the fault location in the neighborhood of the measuring location is generally such that this signal at the measuring location continuously passes through null with change in sign. Therefore there also occurs independent of voltage breakdown, in the case of near faults, under certain circumstances, a considerable uncertainty region for the fault direction determination at the neighborhood of the measuring location.